WASHINGTON -- Nationals top prospect Bryce Harper had to leave Thursday's game against Double-A Akron because of a right hamstring injury. He will be re-evaluated on Friday.

The injury occurred in the eighth inning, according to reports. Harper, who plays for Harrisburg, hurt his hamstring while running from first to third on an Archie Gilbert double. Harper had to be helped off the field.

Harper will likely be placed on the seven-day disabled list, according to a baseball source.

Harper, the first overall pick in the 2010 First-Year Player Draft, is having a solid season, hitting a combined .297 with 17 home runs and 58 RBIs for Class A Hagerstown and Double-A Harrisburg.